Stretching machine for stretching metal sheets and the like



E. MLLER ETAL Marfzh 17, 1964 STRETCHING MACHINE FOR STRETCHING METAL SHEETS AND THE LIKE Filed Feb. 5, 1958 3 Sheets-Sheet 1 @auf f. 5,4%

QAM/ WN ATTORNEY March 17, 1964 E. MLLER ETAL STRETCHING MACHINE FOR STRETCHING METAL SHEETS AND THE LIKE 3 Sheets-Sheet 2 Filed Feb. 3. 1958 March 17, 1964 E. MULLER ETAL 3,125,151

STRETCHING MACHINE FOR STRETCHING METAL SHEETS AND THE LIKE Filed Feb. s, 195s s sheets-sheet :s

u MM ff .d TTORN EY United States Patent() Claims priority, application Germany Feb. '7, 1957 6 Claims. (Ci. 153-35) The present invention relates to machines for stretching sheets of metal or the like.

At the present time machines of this type have several disadvantages. Thus, the parts of conventional stretching machines of the above type must be very large and rugged in order to withstand the forces to which they are subjected during the stretching of a sheet of metal, and

if a sheet of metal tears during the stretching thereof it does not infrequently happen that parts become damaged and become loose from the foundation to which they are fastened.

One of the objects of the present invention is to provide a stretching machine of the above type which is made up of smaller sized parts than a conventional stretching machine capable of exerting the same forces.

Another object of the present invention is to provide a means which will guarantee that the parts will not become damaged or loosened from the foundation when a sheet of rnetal or the like tears during the stretching thereof or when the grip of the machine on the sheet of metal slips during the stretching of the sheet of metal.

A further object of the present invention is to provide a machine of the above type which can be easily adjusted in a stepless manner to be able to take care of any length of a sheet of metal or the like between predetermined maximum and minimum lengths.

An additional object of the presentrinvention is to provide a machine of the above type wherein pressure columns used for transferring the forces during the stretching of a sheet of metal or the like are reliably prevented from buckling during the stretching of a sheet of metal or the like.

Still another object of the present invention is to provide a machine of the above type with a means which will reliably prevent movement of gripping jaws away from each other during the stretching of a sheet of metal or the like.

Another object of the present invention includes the provision of a stretching machine of the above type wherein cylinders of the hydraulic means which produces the stretching force need only be fixed to the support in order to locate the cylinders in the proper positions, none of the stretching forces or the forces which occur when a sheet of metal or the like tears being transmitted to the cylinders in a manner which tends to separate them from their support.

It is also an object of the present invention to provide a structure capable of accomplishing all of the above objects and at the same time composed of simple and ruggedly constructed elements which are very reliable in operation.

With the above objects in View, the present invention includes in a stretching machine for stretching a sheet Vof metal or the like a pair of gripping means for respectively gripping opposite ends of a sheet of metal or the like which is to be stretched and a support means supporting the gripping means for movement away from each other. At least one of these gripping means is supported for movement away from the other of the gripping means, and between the pair of gripping means are located a pair of columns which are parallel and spaced from each other and which extend between and cooperate with the 3,125,151 Patented Mar. 17, 1964 ICC pair of gripping means for moving at least the one movable gripping means away from the other gripping means. In accordance with the present invention, part of each column is formed in between and spaced from the pair of gripping means by a means which cooperates with the columns for increasing the length thereof so that the pair of gripping means will be separated from each other to an increasing extent in order to produce the stretching of a sheet of metal gripped by the pair of gripping means, and because this means which increases the length of the columns is located between and spaced from the pair of gripping means each of the columns is divided into a pair of portions much shorter than a single continuous column extending between the pair of gripping means and therefore far less likely to buckle.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. l is a top plan view showing schematically one possible construction of a stretching machine in accordance with the present invention;

FIG. 2 is a schematic, partly sectional, side elevational view of the stretching machine of FIG. l;

FlG. 3 is an elevational view of a means for reinforcing the gripping jaws of the machine of the invention;

FIG. 4 is a schematic, partly sectional, top plan view of another embodiment of a stretching machine according to the present invention;

FIG. 5 is a sectional side elevational view of the machine of FIG. 4;

FIG. 6 is a fragmentary partly sectional schematic plan view of a Vthird embodiment of a stretching machine according to the present invention; and

FIG. 7 is a schematic sectional view of the hydraulic structure associated with the right end of the machine of FIG. 7 for adjusting the parts -at this right end of. the machine as well as for absorbing shocks which occur during operation of the machine.

Referring now to FIG. l, the stretching machine illustrated therein includes a pair of gripping means 1 which are supported by a suitable support means for movement with respect to each other in a stretching direction away from each other. The `support means includes a oor which xedly carries the parallel rails 3, and a pair of carriages 2 are respectively movable along the rails 3 and respectively carry the pair of gripping means 1. The upper half of FIG. l shows the position which the parts take when the pair of gripping means 1 are at the maximum stretching distance L1 from each other, while the lower half of FIG. l shows the pair of gripping means 1 at their shortest distance L2 from each other.

A pair of parallel spaced columns are located between the pair of gripping means and extend in the stretching direction, and each of the columns includes between its ends which cooperate with the pair of gripping means 1 a hydraulic means which forms part of each column and which serves to increase the length thereof so as to move the pair of gripping means away from each other for stretching a sheet of metal or the like which is respectively gripped at its ends by the pair of gripping means 1. The means for increasing the length of the columns, which forms part of the columns, includes a pair of parallel cylinders which are carried by the support means and which are located opposite and aligned with each other. Each of the cylinders is made up of a pair of cylinder portions 4 and 5 which are coaxial with each other, and

a pair of pistons 6 and 7 are respectively slidable in the pair of cylinders 4 and 5. The pistons 6 and 7 in each cylinder 4, 5 move oppositely with respect to each other through equal distances so that each of the pistons need only move through one-half of the total stretching stroke. This is in distinction to a conventional structure where each piston must move through the entire stretching stroke.

In the example illustrated in FIG. 1 the cylinder which is composed of the cylinder portions 4 and 5 includes a partition 8 located between the portions ftand 5 and forming a pair of cylinder chambers which respectively cooperate with the pistons 6 and 7. Therefore, it is possible with this construction to operate with only one pair of pistons, if desired. By directing equal amounts of hydraulic liquid under pressure at equal rates to the several cylinder chambers all of the pistons will be moved very accurately through equal distances at the saine rates, so that the stretching force will be equally distributed between the pair of gripping means 1 and 2. Also, all four cylinder chambers may communicate hydraulically with each other in order to guarantee that all of the pistons move through equal distances at the same rates.

In accordance with the present invention, the column which cooperates with each cylinder 4, 5 includes a plurality of spacer elements 9 arranged on one side of the cylinder 4, 5 and a plurality of coaxial spacer elements 10 arranged on the other side of the cylinder 4, 5. All of these spacer elements are coaxial with cach other in each column. These spacer elements are removable and simply abut against each other and are used except in the case where the shortest length of metal which is to be stretched is worked on. The spacer elements 9 and 1t) may be inserted into the machine with an overhead crane, for example, or they may be laterally introduced into the machine. As is evident from FIG. 2, each of the spacer elements is supported by a carriage 11 which rolls along rails 12 which extend parallel to the rails 3, these rails 12 cooperating with the carriages 11 to guide the spacer elements for movement along the axis of the column. The removable spacer elements 9 and 1t) which can be removed and exchanged for spacer elements of different lengths make it possible to steplessly adjust the machine for handling sheets of any length in the range between the shortest length L2 and the largest length L1, if each of the pistons 6 and 7 is movable through a stroke which not only is equal to one-half of the total stretching stroke but also is greater than one-half the length of the shortest spacer element. The greater the stroke of each piston with respect to the shortest length of spacer element, the greater the number of spacer elements of different lengths which can be used at one time. The several spacer elements are so short that there is no danger of any spacer element buckling due to the axial pressure applied thereto. The columns bear against the lateral portions 1a of each gripping means 1, and these portions 1a are formed with end faces which respectively form parts of spheres and respectively carry for limited movement with respect to these end faces members 13 which directly engage the outermost spacer elements of the columns, so that in this way any shifting of the gripping means 1 is not transferred to the columns.

Since the structure of the invention does not include one-piece columns connected with the gripping means and since the gripping means do not have any positive connection with the pistons 6 and 7, then it is necessary to provide the gripping means with moving means which will shift the gripping means. This moving means which serves to move the gripping means 1 for the purpose of accommodating sheets of metal of different lengths and for the purpose of inserting and removing spacer elements of the columns takes the form of an elongated piston rod 14 connected to each of the lateral portions 1a of each gripping means 1 and terminating distant from each of the gripping means in a piston 15 which slides in an elongated cylinder 16 carried by the support means and having an axis which is parallel to the axes of the columns. The length of the piston rod 14 as well as the cylinder 16 is great enough to enable the gripping means 1 at each side of the machine to be moved from the position shown at the upper half of FIG. l for accommodating sheets of the longest length to the position indicated in the lower half of FIG. 1 for accommodating sheets of the shortest length, and in the position of the parts shown in the lower half of FIG. 1, there are no spacer elements and the column at each side of the machine is formed solely by the cylinder 4, 5 as well as the pistons 6 and 7 which respectively bear against the elements 13 of the gripping means. At the upper half of FIG. 1 the gripping means 1 is shown spaced beyond the column so that the rails 12 for the spacer elements are visible at the upper portion of FIG. 1. This movement of the gripping means beyond the point where they cooperate with the longest length of sheet which can be accommodated by the machine is necessary in order to disconnect the sheets from the gripping means as well as to connect the sheets to the gripping means.

If it should happen that a sheet should tear while it is being stretched, then it is possible that the parts of the machine would be subject to damage because of the severe shock which would occur by the rapid outward movement of the gripping means away from each other due to the fact that the sheet no longer resisted the movement of the pair of gripping means away from each other, and therefore shock absorbers, safety Valves, or the like are provided in order to absorb the shocks which might occur upon tearing of a sheet during the stretching thereof. In the example which is illustrated in FIG. 1 the shock which occurs upon tearing of a sheet during the stretching thereof is adsorbed by a structure which includes a container 17 for air under high compression and this containei' 17 communicates through suitable conduits with cylinders 19 which form extensions of the cylinders 16, respectively. Within these cylinders 19 are respectively arranged free floating pistons 18 which are urged by the air under pressure within the cylinders 19 toward the gripping means, so that the piston 18 which is shown at the upper left of FIG. l is urged toward the right, as viewed in FIG. 1. At the point where the cylinder 19 is xed to the cylinder 16 is arranged a snap ring 2.0 in a groove in the interior of the connection between the cylinders 16 and 19, and this ring 20 limits the movement of the piston 13 to the right, as viewed in FIG. l, so that the right surface of the piston 18 forms the left end of the cylinder 16. The pressure of the air in the container 17 is great enough to reliably maintain the pistons 1S in the position indicated at the upper left of FIG. 1 during normal operation of the machine. The uid which is introduced into the cylinder 16 ahead of the pistons 15 for shifting the gripping means toward each other does not have a pressure great enough to move the pistons 18 away from the stop rings 20. However, when during the stretching of a sheet of metal or the like, this sheet tears so that the pair of gripping means move rapidly away from each other, the force applied to the pistons 18 between the latter and the pistons 15, respectively, is great enough to move the pistons 18 away from the stop rings 20, respectively, and in this way the air which is under pressure in the cylinders 19 is compressed further and absorbs the forces which occur at this time so that the parts of the machine are not damaged.

Each of the gripping means 1 of the structure of the invention includes upper and lower sheet metal laminations 1b and 1c which are connected together and which serve to support the gripping jaws and the structure for inoving these gripping jaws. Each of the gripping means includes a pair of gripping jaws 21 extending across each gripping means and directly engaging the sheet for gripping the same, and each of the gripping means includes a known structure for moving the gripping jaws Z1 to the right and left, as viewed in FIG. 2, for respectively gripping and releasing an edge of a sheet, this structure which moves the jaws 21 including the links 22 respectively connected to the jaws 21 of each gripping means. Each gripping means further includes the elongated elements 23 extending across each gripping means and having a wedge-shaped cross section so as to cooperate with the jaws 21 in the manner indicated in FIG. 3 for guaranteeing that these jaws move toward each other into a gripping position when the jaws 21 are displaced to the right, as viewed in FIG. l.

As is shown in FIGS. 2 and 3, a special unit according to the present invention is provided for reinforcing the gripping structure formed by the parts 21 and 23, and this unit includes the pair of beams 24 which extend across each gripping means and which respectively engage the members 23, the pair of beams 24 being parallel to each other and held at the proper distance from each other by the spacers 25 which are arranged between the pair of beams 24. A pair of rings 26 are shrunk onto the ends of the beams 24, in the manner shown most clearly in FIG. 3, so as to keep the parts of the unit of FIG. 3 together, and this separate unit cooperates with the remainder of the gripping means to prevent movement of the jaws 21 away from each other so that the sheet material or the like is reliably gripped with this strong structure. It will be noted from FIG. 3 that the distance B Vis provided between the pair of rings 26, and this distance enough to also provide between the beams 24 a suficient vertical distance to accommodate the parts 21 and 23. It will be noted from FIG. 2 that an additional carriage 27 is provided for each gripping means to support the latter while it moves along the guide rails 3 of the support means. As was pointed out above a pair of the piston rods 14 are fixed to each gripping means at opposite sides thereof and cooperate with pistons and cylinders 16 to move each of the gripping means to a selected location on the machine.

It will be noted that the columns of the above-described structure in addition to being of such a short length that buckling cannot occur are composed of elements which have smooth, unthreaded outer surfaces, so that there is no danger of cracks or the like occurring from the formation of threads, for example, in the surfaces of the spacer elements which form the columns. It will also be noted that with the above-described structure the stresses are so distributed among the various elements that none of the parts need be of a particularly massive heavy construction and therefore all of the parts can be easily moved without any especially large structures required for this purpose. The pistons 6 and 7 and the cylinders in which they slide, for example, can be of a smaller diameter than in a conventional machine where a piston and cylinder is arranged at one end of the machine for providing all of the stretching movement.

Of course, it is possible to provide an elongated stationary cylindrical block or the like which takes the place of each pair of aligned pistons 6 and 7 and to arrange movable cylinders 4 and 5 on the ends of such a cylindrical block; in this case, the end walls of such cylinders engageV the columns to move the same. However, the above-described structure shown in the drawings is preferred because it is possible with the structure of the drawings to provide simple hollow cylinders made up of the elements 4 and 5, and end walls of cylinders ture may be operated with either the pistons 6 or the pistons 7.

A further advantage of provlding a pair'of gripping means 1 both of which are movable is that upon tear- -ing of a sheet during the stretching thereof each of the gripping means can be braked independently of the other so that all of the force resulting from the tearing of a sheet during the stretching thereof need not be absorbed by one of the gripping means.

The formation of the columns by the plurality of spacer elements 9 and 10 is of particular advantage not only with respect to the fact that these relatively short spacer elements can easily be moved about, as compared, for example, with long one-piece columns, but in addition each of the spacer elements need only be finished at its outer surface and at its ends, and the inner surface of each of the relatively thick walled tubular spacer elements need not be finished and may be left as it comes from the mold in which it was cast, so that the spacer elements which form the columns are relatively inexpensive to manufacture.

Of course, a hydraulic moving means for each of the gripping means 1 need not be provided, and instead any suitable mechanical moving means may be used such as a suitable rack and pinion, for example, but the disclosed hydraulic moving means is preferred since it provides the advantage of a relatively long braking movement of each gripping means when a sheet tears during the stretching thereof, and furthermore it enables the shock absorbing structure 17-19 to be provided in a very simple manner.

As is apparent from the above description of the gripping means, not only are stresses applied to the gripping means in a horizontal direction during the stretching of a sheet, but in addition the jaws 21 tend to move away from each other in a vertical direction so as to provide vertical stresses. The result is that a conventional gripping means is made up of an extremely complicated large casting which is designed to take care of both the horizontal and the vertical stresses. By providing the separate unit shown in FIG. 3 designed only to take up the vertical stresses resulting from the tendency of the jaws 21 to move in a vertical direction away from each other, the structure of each gripping means is considerably simplified and the gripping means of the present invention is far less expensive than a conventional gripping means. The parts which make up each of the gripping means 1 of the present invention are of lighter weight than the structure of a conventional gripping means, and furthermore since the unit of FIG. 3 is designed for only vertical forces while the remainder of the gripping means is designed for horizontal forces, the structures can be far more accurately designed so that they can be strong enough while still being of a lighter Weight and simpler construction than a conventional gripping means.

In the structure which is illustrated in FIGS. 4 and 5 the pairs of gripping means 31 and 32 are identical with the above-described pair of gripping means 1, and they are supported by carriages 33 on the rails 34 of the support means for movement to the right and left, as viewed in FIGS. 4 and 5. The upper half of FIG. 4 shows the pair of gripping means in most distant position from each other, the upper half of FIG. 4 showing the position which the parts take to accommodate a sheet of the longest length, while the lower half of FIG. 4 shows the position which the parts take while working with a sheet of the shortest length which can be handled by the machine.

The pair Vof columns of the embodiment of FIGS. 4 and 5 include the means inserted into and forming part of the columns for increasing the length thereof, as was the case with the embodiment of FIGS. l-3, and in the embodiment of FIGS. 4 and 5 the support means carries a pair of parallel cylinders 35 which are located opposite and aligned with each other between the pair of gripping means 31 and 32. A piston 36 is slidable within each of the cylinders 35 and these pistons 36 press against the elongated coaxial column portions 37 which are located to the left of the cylinders 35, as viewed in FIGS. 4 and 5. It will be noted that the column portions 37 are relatively short in that they do not extend across the entire space between the pair of gripping means 31 and 32, so that in this way the danger of buckling is greatly reduced or eliminated. At the right side of the cylinders 35, as viewed in FIGS. 4 and 5, are located the relatively short column portions 38 which are coaxial with the column portions 37, respectively, and these column portions 38 remain stationary and cooperate with the gripping means 32 which remains stationary during the actual stretching of the sheet of metal or the like but which can be shifted between the positions shown in the upper and lower portions of FIG. 4 before the actual stretching takes place.

For the purpose of adjusting the machine to sheets of different lengths, the columns 37 are each `formed in their outer surface with an annular `groove means which may be in the Kform of a single continuous helical groove in the nature of a thread, but which preferably is in the form of a plurality of independent closely spaced annular grooves of relatively small depth. A split nut means 39 cooperates with the grooved outer surface of each column 37 for adjustably connecting the gripping means 3d to the columns 37. Each of the split nut means 39 is carried by a portion 31a of the gripping means 31 and is provided throughout its length -lwith grooves which receive the projections between the grooves of the column 37. -Although each individual annular groove and the rib of the split nut which enters the same is of relatively small size, the rela tively large number of these grooves and ribs provides the necessary area for maintaining the gripping means 3i operatively connected with the columns 37 and for efficiently transmitting the relatively high forces between the columns 37 and the gripping means 3l. Each `split nut means 39 is in the form of a pair of nut halves, as shown in the lower portion of FIG. 4, turnably supported by a pin 4i) carried by the gripping means 31. The two halves of each split nut 39 are turnable transversely away from the column 37 upwardly to an inoperative position which disconnects the gripping means 3l from the column 37 so that the gripping means 31 may then be shifted to a desired position along the columns 37, and then the two hal-ves of the split nut are turned downwardly to their operative position where they cooperate with the grooves of the column 37 to interconnect the gripping means 3l with the columns 37. Instead of a split nut, the nut 39 may take the form of a one-piece annular nut, and in this case the grooves and ribs are interrupted by axially extending grooves, while the outer surface of the column 37 is also formed with axially extending grooves, and with this construction the nut 39 is turned to locate its grooves and projections aligned with the axial grooves of the column 37 so that the nut 39 together with the gripping means 31 can then be shifted :axially along the column37, and then a slight turning of the nut 39 locates its grooves and ribs in cooperation with the grooves and ribs of the column 37 to provide the interconnection between the gripping means 3l and the columns 37, so that this construction operates in the nature of a bayonet connection between the gripping means 3l and the columns 37.

During the operation of the structure of FIGS. 4 and 5, the gripping means 32 cooperates with one of a pair of shoulders on each column 33 so that the -gripping means 32 cannot move to the left, as viewed in FIG. 4, and the stretching is provided by advancing the pistons 36 together with the columns 37 to the left so as to move the gripping means 3]; to the left, as viewed in FIGS. 4 and 5 in order to produce the desired stretching of a sheet gripped between the gripping means 3l and 32. It will be noted that this system is self-contained and therefore the cylinders 35 do not have to be ixedly connected to the foundation. Moreover, it will be noted that the pistons 36 are stepped, so that they can be moved to the right, as viewed in FIG. 4, by introducing the fluid under pressure against the annular surface of each piston which is opposite the right end face thereof, as viewed in FIG. 4. If a sheet of metal or the like should tear during the stretching thereof, then the sudden movement of the gripping means 3l to the left, as viewed in FIG. 4, would cause the stepped pistons 35 to strike against the left end walls of the cylinders 35, as viewed in FIG. 4, and this would produce a tremendous force acting on the cylinders 35 which might injure the same and which would also require that these cylinders 35 be iixedly and lirmly connected with the foundation. In order to avoid such transmission cf heavy forces to the cylinders 35 when a sheet tears during the stretching thereof, the pistons 36 are not positively connected with the columns 37 and instead only press against these columns to move the same to the left, as viewed in FIG. 4, the columns 37 not participating in the movement of the pistons 36 to the right, as viewed in FIG. 4. The gripping means 3l is formed with a pair of openings through which the columns 37 respectively pass, each column 37 extending beyond both the front and the rear of the gripping means 3l, and as is particularly evident lfrom FIG. 5, suitable carriages 4I are connected with the ends of each column 37 at the front and rear of the gripping means 3i and cooperate with suitable rails for guiding each column 37 for axial movement.

The portions 32a of the gripping means 32 are formed with parallel openings through which the columns 3S respectively pass, and each column 33 is provided at its left end, as viewed in FIG. 4, with an enlarged portion 42 which abuts directly against the right end of the cylinder 35, as viewed in FIG. 4, so that this enlarged portion 42 forms an annular shoulder of the column 38 against which the gripping means 32 bears when the gripping means 32 is in the position shown in the lower half of FIG. 4 for accommodating a sheet of short length. Midway between its ends each column 33 is provided with a portion of reduced diameter which provides a second shoulder distant from the shoulder provided by the enlarged end 42 of each column 3S, and the gripping means 32 is shown in FIG. 4 cooperating with this second shoulder so that it cannot move further to the left beyond the position shown in the upper half of FIG. 4. By placing the gripping means 32 in either of the positions shown in the upper and lower halves of FIG. 4 and by selectively placing the split nut means 39 in connection with any desired set of the closely spaced annular grooves of the columns 37, it is possible to arrange the gripping means 31 and 32 with respect to each other in order to accommodate sheets of any desired length within the range of maximum and minimum lengths which can be accommodated by the particular machine. The gripping means 32 carries a split sleeve means 43 which is identical with the split nut means 39 except that it has an inner smooth surface, and these halves of the split sleeve 43 can be turned upwardly away from the column 33 for disconnecting the gripping means 32 from the column in order to shift the gripping means 32 with respect to the columns 38. In the lower half of FIG. 4 the split sleeve 43 is shown engaging the enlarged portion 42 of the lower column 38 of FIG. 4, while in the upper half of FIG. 4 the split sleeve 43 is shown engaging the shoulder which is midway between the ends of the column 38 shown in the upper half of FIG. 4. The ends of the columns 38 which are distant from the cylinders 35 are directly supported on the foundation. A moving means identical with that of FIGS. l and 2 is operatively connected with each of the carriages or gripping means 31 and 32 for moving the latter, and as may be seen from FIG. 5, this moving means includes the elongated cylinder 44 which corre- Ysponds to the cylinder I6 and which receives the elongated piston 45 directly connected with the gripping means 3l. The cylinder 44 has an extension which cooperates With a source of compressed air 47 in the same way as the cylinder 19, and this extension receives a free iioating piston 48 which corresponds to the piston 1S, a

stop ring 50 being located at the left end of the cylinder 44 to prevent the piston 43 from moving to the right beyond the position shown in FIG. 5, so that this structure of FIG. is the same as the corresponding structure of FIG. 1 and operates in the same way. Thus, in the event that a sheet tears during the stretching thereof the pistons 48 will yield in their respective cylinders in order to absorb the shock.

It will be noted that each of the cylinders 35 is in the form of a simple hollow metal cylinder which is open at both ends, so that the construction of each cylinder 35 is quite simple and each of the cylinders can be formed from forged steel. A separate wall 51 is located in each of the cylinders 35 and is prevented from moving to the right, as viewed in FIG. 4, by a snap ring 52 located in a suitable groove formed in the inner surface of the cylinder 35.

With the construction of FIGS. 4 and 5, it will be noted that by arranging the cylinder 35 and piston 36 of each column between the ends thereof, the column portions at each side of the cylinder 35 are relatively short and in this way the danger of buckling is also prevented. The provision of a single set of pistons 36 is of advantage in that the number of piston rings and sealing glands is reduced by one-half, as compared with the embodiment of FIGS. 1 and 2. While a plurality of spacer elements could be used for the columns of FIGS. 4 and 5, the arrangement shown does not present any particular disadvantage because the columns 33 remain stationary and are not provided with any sort of grooves or threads or the like, and it is only necessary to provide the columns 37 with the annular grooves, so that this construction of FIGS. 4 and 5 is still far superior to a conventional construction where a single one-piece elongated column must be provided with a great number of threads.

The special moving means which cooperates with the gripping means 3l for moving the same is required because of the fact that there is no positive connection with the pistons 36. However, if such a positive connection were provided then it would be unnecessary to provide the gripping means 31 with a separate moving means. In order to take care of the case where a sheet tears during the stretching thereof, the connection between the pistons 36 and the columns 37 in such a construction would have to be such that it would automatically become disconnected upon tearing of a sheet. Therefore, the disclosed construction described above and shown in FIGS. 4 and 5 is preferred because of its relative simplicity as compared to a construction where there would necessarily be provided between the pistons 36 and the columns 3'7, respectively, a special connecting structure which would automatically release the columns 37 from the pistons 36 upon tearing of a sheet of metal during the stretching thereof.

It is possible, of course, to provide sets of interchangeable stationary columns 38 of dierent lengths so that the position of the gripping means 32 can be controlled by removing one set of columns 38 and replacing them with another set of different lengths. However, the abovedescribed arrangement is preferred because it still provides diierent positions for the gripping means 32 and at the same time does not require removal of the columns 38.

In spite of the above-described arrangement of closely spaced annular grooves in the columns 37 the structure of FIGS. 4 and 5 is steplessly adjustable to different lengths of sheets within the range of length which can be handled by the machine. This result is brought about by giving to the pistons 36 a stroke which exceeds the maximum stretching stroke by a distance greater than or at least as great -as the space between a pair of adjacent annular grooves of each column 37. In this way the pistons 36 themselves may be shifted so as to take care of the range of sizes between those provided by the annular grooves of the columns 37, and thus with this construction the machine is also steplessly adjustable to sheet lengths anywhere within the range between the minimum and maximum sheet lengths capable of being handled by the machine.

It will be noted that with the above-described construction there is no turning between the split nut means 39 and the column 37, and this construction is also preferred because with this arrangement it is possible to make both the columns 37 as well as the split nuts 39 out of steel without any danger of the parts becoming worn due to turning of one of the parts with respect to the other, as would be the case if a conventional nut cooperated with threads on the columns 37. Thus, this construction is particularly suitable for those cases where because of the relatively large forces which are transferred between the columns 37 and the gripping means 31 it is necessary to use exceedingly strong materials both for the columns 37 as well as for the split nut halves 39, since with the construction of the invention there is no fear of wear between these parts. The carriages 41 render the columns 37 sel-fsupporting when they are disconnected from the gripping means 31.

Referring now to FIGS. 6 and 7, the pair of gripping means 61 and 62 illustrated in FIG. 6 are identical with the gripping means 31 and 32 of F-IG. 4 and are supported for movement in the same way. The pair of gripping means 6I and 62 are shown in FIG. 6 in the positions which they take when they are closest to each other and capable of handling the shortest length of sheet which can be accommodated by the machine. With the embodiment of FIG. 6, as is the case with the above-described embodiments, the pair of columns whose axes are located in the stretching plane are each made up in part of the means located between the ends of each column for increasing the length thereof, and this means in the embodiment of FIG. 6 takes the form of a pair of simple cylinders 63 having opposite open ends and connected to the foundation so that they are parallel to each other and located opposite and aligned with each other, only one of the cylinders 63 being shown in FIG. 6. Pistons 64 respectively slide in the cylinders 63 for increasing and decreasing the length of the columns, and it will be noted that the column portions 65 and 66 at the opposite ends of the cylinders 63 are shorter than would be the case if the cylinders 63 were arranged at one end of the column, so that in this way the structure of FIG. 6 also prevents buckling of the columns by reducing each column to portions of relatively short lengths. VIn the embodiment of FIG. 6, the columns 66 which correspond to the stationary columns 33 of FIG. 4 `are respectively connected with piston 67 which extend slidably into the cylinders 63, respectively, at the right ends thereof, as viewed in FIG. 6. In the illustrated position of the parts, only relatively short lengths of the columns 66 and 65 are effective due to the positioning of the pair of gripping means 61 and 62 at the shortest possible distance from each other, as shown in FIG. 6. In a manner which is described below, a suitable means in accordance with the present invention cooperates, through the columns 66, with the pistons 67 for maintaining the latter axially immovable during the actual stretching of a sheet, so that the entire stretching of a sheet during normal operation of the machine takes place as a result of axial movement of the pistons 64. The pressure of the hydraulic fluid in the common chamber between the pistons 64 and 67 is transmitted through the pistons 67 and the columns 66 to the gripping means 62 which remains stationary during the actual stretching of a sheet of metal or the like, as is the case with the gripping means 32 of FIG. 4. The gripping means 62 is provided with a pair of split sleeve means 69 corresponding to the split sleeve means 43 of FIG. 4 and constructed in the same Way to cooperate with the portion of the column 66 shown in FIG. 6 next to the split sleeve means 69 or cooperating with a shoulder intermediate the ends of the column 66 when the gripping means 62 is located in a position corresponding to that shown in the upper half of FIG. 4, and in this way in either of the positions of the gripping means 62 the pressure of the fluid which engages the pistons 67 in the cylinders 63 is transmitted through the columns 66 back to the gripping means 62. The columns y65 of FIG. 6 are the movable columns of this embodiment and correspond to the columns 37 of FIG. 4, and these columns 65 may be provided with annular grooves or the like in the same way as the columns 37 and cooperating with a split nut means 7 carried by the gripping means 61 and having a construction identical with the split nut means 39 of FIG. 4, so that the gripping means 61 may be selectively connected at any point along the columns 65 to be connected therewith to be moved by the pistons 64 when the latter move outwardly of the cylinders 63. If desired, the connection between the movable columns 65 and the gripping means 6l may be provided through suitable teeth formed in the columns 65 and cooperating with pawls carried by the gripping means 6I for transmitting the movement of the columns to the gripping means 61 while enabling the latter to be connected selectively to the columns 65 at desired positions therealong.

Each side 61a of the gripping means 61 cooperates with a hydraulic moving means and shock absorbing means for moving the gripping means 61 and for absorbing shocks when a sheet tears, and the gripping means 62 is also provided at each of its sides 62a with an identical moving means, the details of this moving means being shown in FIG. 7. As may be seen in FIG. 7, an elongated piston rod 71 is connected with each side of each gripping means, and the piston rod '71 is connected with a piston 72 which is slidable within an elongated stationary cylinder 73 xedly carried by the support means and having a length corresponding to the longest distance through which each of the gripping means must be shifted. The right end of the cylinder 73, as viewed in FIG. 7, is closed by a free floating piston 74 slidable within an extension 75 of the cylinder 73, and the movement of the piston 74 to the left, as Viewed in FIG. 7, is limited by the stop ring 77 which is located between the cylinders 73 and 75 in the manner shown in FIG. 7. The interior of the cylinder 75 communicates with a tank 76 of compressed air so that the compressed air urges the piston 74 to the left, as viewed in FIG. 7, to maintain the piston in engagement with the stop ring 77. The pressure applied against the piston 74 by the compressed air in the tank 76 is great enough to prevent movement of the piston 7 4 to the right, as viewed in FIG. 7, when liquid under pressure is introduced into the cylinder 73 to the right of the piston 72 through the conduit 78 when the valve 79 is opened, so that in this way the liquid under pressure acts on the pistons 72 for moving the gripping means with which its piston rods 71 are connected, and the piston 74 does not move at this time. Thus it is possible to shift the gripping means with this hydraulic moving means. When the gripping means is to be moved in the reverse direction, the liquid under pressure is introduced through the conduit 86 into the cylinder 73 at the left side of the piston 72, as viewed in FIG. 7, the valve 81 being open at this time, and the valve 83 is also open at this time so that the liquid in the cylinder 73 to the right of the piston 72 may flow through the conduit 82 back to the reservoir 84. While FIG. 7 shows the construction for moving the gripping means 62, it will be understood that an identical construction is used for moving the gripping means 6I. Also, during the actual stretching of a sheet of metal or the like the valve 83 is opened.

If a sheet of metal or the like should tear during the stretching thereof, then the gripping means 6I and 62 will have a tendency to ily apart from each other, and at this time the open valves 83 throttle the flow of the hydraulic fluid back to the tank 84 so that the pressure of the liquid in the cylinders 73 ahead of the pistons 72 increases tremendously to cause the pistons 74 to move away from the stop rings 77, respectively, into the cylinders 75 l2 against the force of the compressed air, and in this way the shocks which occur upon tearing of a sheet of a metal or the like during the stretching thereof are absorbed.

In the case where the means 70 for connecting the gripping means 61 with selected portions of the moving columns 65 is replaced by one or more pawls which cooperate with one of a series of teeth formed in the co1- umn 65 and having the configuration of ratchet teeth, the columns 65 are fixedly connected with the pistons 64, respectively, and the pawl and ratchet-tooth type of connection between the gripping means 6l and the columns 65 is such that the gripping means 61 is free to move to the left, as viewed in FIG. 6, with respect to the columns 65 which can remain stationary at this time together with the pistons 64, while the pistons 64 together with the columns 65 are moved to the left by the fluid under pressure in the cylinders 63 and, the movement is transmitted through the pawls -to the gripping means 61. With such a construction, upon tearing of a sheet of metal or the like during the stretching thereof, the gripping means 6I will move to the left without the columns 65 and pistons 64, and the columns 65 and pistons 64 in this case are provided with a hydraulic moving and shock absorbing means identical with those described above in connection with the pair of gripping means 6l and 62 although having a much shorter stroke.

Inasmuch as the columns 66 on the opposite side of the cylinders 63 from the columns 65 remain stationary at all times they do not require any moving means to be connected therewith and require only a suitable means for determining the positions of the pistons 67 during normal operations and for absorbing shocks which occur upon tearing of a sheet of metal or the like during the stretching thereof. This structure which is connected through the columns 66 with the pistons 67 is shown in detail in FIG. 7. Each of the columns 66 is provided with an elongated portion 66a of a smaller diameter than the remainder of each column 66 to provide the shoulder intermediate the ends of each column 66, and these hollow portions 66a of the columns 66 are connected through rods with pistons 86 which are slidable within cylinders 87 xedly carried by the support means. The means 68 which thus cooperates through each column 66 with each piston 67 has its cylinder 87 in communication with the -tank 76 of air at high pressure, and this air maintains the piston 86 against the end wall 88 of the cylinder 67 during normal operation so that in this way the position of the piston 67 is fixed axially and remains unchanged during the normal operation of the machine, the pressure provided through cooperation of the compressed air with the pistons 86 being great enough to prevent movement of the pistons 67 to the right, as viewed in FIG. 6, during the stretching of a sheet of metal or the like. If, however, as a result of tearing of a sheet of metal or the like during the stretching thereof, or as a result of slipping of the gripping means with respect to the sheet of metal or the like, large forces suddenly occur, then these forces can be absorbed by movement of the pistons 67 to the right, as viewed in FIG. 6, with yielding of the pistons 86 in the cylinders S7 to absorb the forces, the par-ts being so designed that at this time the pistons 67 do not move all the way out of the cylinders 63. It will be noted that both the pistons 67 as well as the pistons 64 are in the form of simple plungers having cylindrical outer surfaces of constant diameter. Of course, as soon as the momentary shock is absorbed, the compressed air in the cylinders 87 shifts the pistons S6 back to the position shown in FIG. 7 so as to return the pistons 67 to their original position. It will be noted that with this construction there are absolutely no axial forces applied to the cylinders 63, and these cylinders 63 need only be connected to the support means so as to have their positions determined. Special strong connections for the purpose of transmitting forces from the cylinders 63 through the support means to the foundation are com- 13 pletely unnecessary with the construction of FIGS. 6 and 7.

The pair of gripping means 61 and 62 are maintained parallel to each other by equal transmission of the hydraulic uid to and from the cylinders 73 so as to move the gripping means 61 and 62 at all times equally at their opposite sides so as to prevent lateral turning of one of the gripping means about a vertical axis with respect to the other of the gripping means. However, if desired, the hydraulic circuit may be provided with an automatic control which automatically compensates for any tendency of one of the gripping means to turn about a vertical axis by causing automatic leakage of the hydraulic fluid from the proper cylinders 73 or in some other manner automatically preventing either of the gripping means 62 from taking a position where it is improperly oriented with respect -to the remaining structure of the machine.

It will be noted that the above-described structure of FIG. 6 does not require any connection between the cylinders 63 and the support means which is strong enough to absorb shocks which occur upon tearing of a sheet during the stretching thereof, for example. Of course, since the pistons 64 are in the form of simple cylindrical plungers, it is necessary to provide the above-described moving means for the columns 65 which are connected to the pistons 64, so that in this way it is possible to move the columns 65 together with the pistons 64 to the right, as is viewed in FIG. 6, to their starting position.

It would be possible to provide a suitabley spring arrangement for absorbing the shock applied to the pistons 67. For example, instead of the above-described pneumatic arrangement, it would be possible to provide a series of dish springs capable of yielding to absorb the shock upon tearing of a sheet of metal during the stretching thereof. However, with such an arrangement the spring structure would yield slightly when the pressure of the hydraulic fluid acting on the pistons 64 increases to shift these pistons outwardly of the cylinders 63, respectively, and therefore the positions of the pistons 67 would not be xed from the very beginning of the stretching process. For this reason the above-described structure shown in detail in FIG. 7 is preferred, since with this construction the position of the pistons 6'7 remains unchanged from the very beginning of the stretching process.

With all of the above-described embodiments of the invention suitable hydraulic circuits are provided, these circuits including suitable valves, pumps, reservoirs, and the like to move the pistons in lthe required manner so as to properly operate the machine. Since such hydraulic systems are well known they have not been shown in the drawings or described, in the interest of conciseness.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of sheet stretching machines differing from the types described above.

While the invention has been illustrated and described as embodied in adjustable stretching machines, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. A stretching machine for stretching sheets of metal and the like, comprising, in combination, support means; a pair of gripping means located in a given plane for respectively gripping the ends of a sheet of metal or the like which is to be stretched, said pair of gripping means being supported by said support means for movement in said plane away from each other to stretch a sheet of metal or the like; a pair of substantially parallel columns llocated in said plane between said pair of gripping means and being spaced from each other, each column having a pair of opposite ends respectively engaging said pair of gripping means; hydraulic means located substantially midway between the ends of each column and forming part of each column for increasing the length of each column to move said pair of gripping means away from each other, said hydraulic means increasing the length of said columns substantially equally at each side of said hydraulic means, each of said columns comprising, in addition to said hydraulic means, a plurality of coaxial spacer elements arranged in a row and capable of being exchanged for other spacer element-s of different sizes; and guide means supporting said spacer elements for movement along the axes of the respective columns.

2. A stretching machine for stretching sheets of metal or the like, comprising, in combination, support means; a pair of gripping means for respectively gripping the ends of a sheet of metal or the like which is to be stretched, said pair of gripping means being supported by said support means for movement away from each other; a pair of hydraulic cylinders carried by said support means between said pair of gripping means, said cylinders being spaced from each other and respectively having parallel axes and each cylinder having opposite open ends respectively directed toward said pair of gripping means; a pair of pistons slidable in each cylinder along the axis thereof; and a plurality of spacers arranged along the axis of each cylinder on each side thereof and extending between the pistons in each cylinder and said pair of gripping means so that when iiuid under pressure is introduced into each cylinder between the pistons therein to move said pistons away from each other the movement of the piston-s will be transmitted through said spacers to said pair of gripping means for moving the latter away from each other, said spacers being of different lengths and being exchangeable for spacers of different lengths and each piston having a stroke which is equal at least to one-half of the largest stretching stroke and one-half the length of the shortest spacer, so that the machine is steplessly adjustable to accommodate sheets of all lengths within a given range.

3. A machine for stretching sheets of metal or the like, comprising, in combination, support means; a pair of gripping means for respectively gripping the ends of a sheet of metal or the like which is to be stretched, said pair of gripping means being supported by said support means for movement away from each other; a pair of columns parallel to and spaced from each other and arranged between and engaging said pair of gripping means, each of said columns being composed in part of a plurality of elongated hollow tubular spacer elements; and means located substantially midway between the ends of and forming part of each column for increasing the length thereof so as to move said gripping means away from each other to stretch a sheet of metal or the like gripped thereby.

4. A stretching machine for stretching sheets of metal or the like, comprising, in combination, support means; a pair of gripping means for respectively gripping the ends of a sheet of metal or the like which is to be stretched, said pair of gripping means being carried by said support means and the latter supporting at least one of said gripping means for movement away from the other of said gripping means; a pair of spaced parallel columns located between said pair of gripping means, each column having a pair of opposed portions engaging said pair of gripping means; means located between said portions of and forming part of each column for increasing the length thereof so as to move said one gripping means away from said other gripping means to stretch a sheet of metal gripped at its ends by said pair of gripping means, respectively; an elongated cylinder carried by said support means on the side of said one gripping means opposite from said pair of columns and having an axis parallel to said columnsra rst piston slidable in said cylinder and connected to said one gripping means for moving the latter when said rst piston moves in said cylinder; a second piston located in said cylinder at the side of said first piston opposite from said one gripping means; a source of air under pressure communicating with the interior of said cylinder at the side of said second piston opposite from said rst piston for urging said lsecond piston toward said rst piston; and stop means located in said cylinder for limiting the movement of said second piston toward said first piston, so that when a sheet of metal or the like tears during the stretching thereof the movement of said one gripping means away from the other of said gripping means will cause said second piston to move away from said irst piston to absorb the forces of said one gripping means.

5. In a machine for stretching sheets of metal or the like, in combination, support means; a gripping means supported by said support means for movement in a stretching direction, said gripping means gripping an end of a -sheet of metal or the like during stretching thereof and said gripping means including a pair of gripping jaws at least one of which is movable with respect to the other in a direction substantially perpendicular to said stretching direction for gripping an endy of a sheet of metal or the like; and -frame means forming part of said gripping means and located in the region of said jaws thereof for absorbing only forces which tend to move said one jaw away from the other of said jaws to prevent said jaws from releasing a sheet of metal or the like during the stretching thereof, said frame means including a pair of elongated parallel beams between which said pair of jaws are located, and a pair of rings respectively shrunk onto the ends of said beams for preventing movement thereof away from each other and from the remainder of said gripping means.

6. In a machine as recited in claim 5, a pair of spacer means located between said pair of beams adjacent the ends thereof for determining the distance therebetween.

References Cited in the iile of this patent UNITED STATES PATENTS 191,100 Braukman et al May 22, 1877 823,711 Thielmann .Tune 19, 1906 1,962,944 Spatta June 12, 1934 2,269,549 Oeckl Jan. 13, 1942 2,346,213 Flowers Apr. 11, 1944 2,352,442 Loewy et al June 27, 1944 2,357,873 Bower Sept. 12, 1944 2,852,062 Lorant Sept. 16, 1958 FOREIGN PATENTS 371,285 Great Britain Apr. 21, 1932 

1. A STRETCHING MACHINE FOR STRETCHING SHEETS OF METAL AND THE LIKE, COMPRISING, IN COMBINATION, SUPPORT MEANS; A PAIR OF GRIPPING MEANS LOCATED IN A GIVEN PLANE FOR RESPECTIVELY GRIPPING THE ENDS OF A SHEET OF METAL OR THE LIKE WHICH IS TO BE STRETCHED, SAID PAIR OF GRIPPING MEANS BEING SUPPORTED BY SAID SUPPORT MEANS FOR MOVEMENT IN SAID PLANE AWAY FROM EACH OTHER TO STRETCH A SHEET OF METAL OR THE LIKE; A PAIR OF SUBSTANTIALLY PARALLEL COLUMNS LOCATED IN SAID PLANE BETWEEN SAID PAIR OF GRIPPING MEANS AND BEING SPACED FROM EACH OTHER, EACH COLUMN HAVING A PAIR OF OPPOSITE ENDS RESPECTIVELY ENGAGING SAID PAIR OF GRIPPING MEANS; HYDRAULIC MEANS LOCATED SUBSTANTIALLY MIDWAY BETWEEN THE ENDS OF EACH COLUMN AND FORMING PART OF EACH COLUMN FOR INCREASING THE LENGTH OF EACH COLUMN TO MOVE SAID PAIR OF GRIPPING MEANS AWAY FROM EACH OTHER, SAID HYDRAULIC MEANS INCREASING THE LENGTH OF SAID COLUMNS SUBSTANTIALLY EQUALLY AT EACH SIDE OF SAID HYDRAULIC MEANS, EACH OF SAID COLUMNS COMPRISING, IN ADDITION TO SAID HYDRAULIC MEANS, A PLURALITY OF COAXIAL SPACER ELEMENTS ARRANGED IN A ROW AND CAPABLE OF BEING EXCHANGED FOR OTHER SPACER ELEMENTS OF DIFFERENT SIZES; AND GUIDE MEANS SUPPORTING SAID SPACER ELEMENTS FOR MOVEMENT ALONG THE AXES OF THE RESPECTIVE COLUMNS. 